It depends on your preferences. Generally people don’t like to handle too much stuff in the Level Blueprint, but for smaller projects I think it is perfectly fine to use. On the other hand, if this ‘torch needs to be turned on to open gate’ system is something you use several times, it is definitely a good idea to make it in a separate Blueprint.
Unfortunately, I do not have anything similar right now, but if you really can’t get it to work I can make a simple example setup for you tomorrow.